Many electronic assemblies contain components which are sensitive to radio frequency (RF) signals or which emit RF signals. RF interference, also known as electromagnetic interference (EMI), is an extremely important issue in determining the functionality and proper performance and conformance to regulations of electrical assemblies. Many components included within a printed circuit board (PCB) assembly may emit RF signals and numerous regulations exist which limit the amount or extent of RF emission that may occur from an electrical or electronic device. In addition, certain components contained within the PCB assembly may be sensitive to RF interference. In order to comply with regulations and to protect sensitive components from RF interference, RF shields are often placed around the critical components. A RF shield is a conductive structure (typically metal) that prevents radio frequency electromagnetic radiation from entering, leaving, or passing through the shield.
One particular problem associated with PCB design is in establishing an effective means for providing shielding for a RF connector at the point at which the connector is attached to the PCB. RF connectors are used to provide a signal path for a PCB input, or for a PCB output, over a cable (e.g., a RF signal over a coaxial cable) or other signal conveying medium (such as twisted pair, ribbon cable, etc.). Generally, the cable and the RF connector itself are adequately shielded, the shielding incorporated as a function of the design and manufacture of the of the cable or connector. The RF connector is attached to the PCB by a variety of methods, including, but not limited to, soldering, press-fit, epoxy, and thread and nut assembly. Each RF connector must be able to convey the signal transported to or from the cable through the connector and to the specified PCB location via a connector pin. The connector pin is typically soldered to a PCB conductive pad at the point at which the signal is to be received. The point at which the connector pin attaches to the PCB is a possible RF radiating point, and in PCB circuits which are particularly sensitive to nearby RF emission, the radiating connector pin must be shielded.
Prior art RF shields used for shielding radiating connector pins connected to a PCB typically have a shielding member mounted on the side of the PCB from which the radiating pin protrudes. The shielding member is typically a folded metal housing enclosing the radiating pin, the shield member having extension tabs or protrusions from the shield which either are press fit through slots provided in the PCB (through-hole mount) or soldered to a conductive pad proximal to and surrounding an aperture through which the radiating pin projects or protrudes (surface mount). FIGS. 1 and 2 are illustrative of two such prior art shields.
FIG. 1 is an enlarged perspective illustrating a prior art rectangular folded metal RF shield 2 with a compression fit cover 4. Rectangular folded metal RF shields 2 are often referred to as a "cans" and they are frequently used to shield discrete RF emitting components in addition to RF radiating pins. The rectangular frame 6 of the shielding device is stamped and cut from a conductive metal and then folded into a rectangular form. The cover 4 is also stamped and cut from a conductive metal, typically the same material used for the rectangular frame 6, and the planar dimensions of the cover 4 are chosen so that the cover 4 extends at least to each edge of the folded rectangular frame 6. One method for securing the cover 4 to the rectangular frame 6 by providing the cover 6 with extension tabs 8. The extension tabs are folded downward greater than ninety degrees past the planar surface of the cover 4, so that they exert pressure on the sides of the rectangular frame 6, thus properly positioning the cover 6 over the rectangular frame 6 and additionally holding the cover 4 in place. Protrusions 10 are provided along the PCB mating edge of the rectangular frame 6 to hold the shield in place against the PCB. The shield 2 is press fit or through-hole mounted by fitting each of the protrusions 10 within slots provided in the PCB. Alternatively, the shield 2 may be surface mounted to a PCB by bending each of the protrusions 10 outward approximately ninety degrees from the interior of the shield cavity. Each of the protrusions 10 is then soldered to a PCB conductive pad.
A second alternative prior art shielding device, an integral one-piece circular folded metal RF shield 12, is illustrated in FIG. 2. Shield 12 is stamped from a single planar sheet of conductive metal and then folded to provide a shield cavity within. Protrusions 16 extending outwardly from the circular top planar portion 14 are folded downward. The shield 12 is press fit or through-hole mounted to a PCB by fitting each of the protrusions 16 within slots provided in the PCB. Various other devices and topologies are also utilized, as is known in the art; each cut, stamped, and folded from a planar sheet of conductive metal to provide a cavity within the interior of the shield.
One common goal among designers and manufacturers of electric and electronic devices often is to minimize the overall size, weight, and dimensions of the product being manufactured, especially when a prospective consumer desires the characteristics of compactness and mobility in a particular product. Therefore, electronic products which include printed circuit boards within their design have progressively increased the density of designed components within a printed circuit board, increased the use microchips and increased the circuit and component density of utilized microchips, and limited the use of discrete components to supplement circuit design. Additionally, circuit designs which minimize the total number of components utilized without affecting product performance are also important. Materials used to construct non-electronic components, such as the product casing and user interface controls, are also minimized, both to reduce the size and weight of the completed product. Electrical and electronic products which incorporate PCBs emitting RF energy from a radiating terminal or connector pin and which require RF shielding surrounding the radiating terminal or connector pin to protect proximal RF sensitive circuitry therefore have a corresponding need to reduce the size and weight of material utilized to provide the RF shielding.